The present invention relates to a plate lockup apparatus, arranged in a plate cylinder of a printing press, for fixing leading and trailing ends of a plate wound around the circumferential surface of the plate cylinder.
A gap having almost a rectangular section and a length almost equal to the overall length of a plate cylinder is formed in the circumferential surface of the plate cylinder for each of a variety of printing presses. A plate lockup apparatus consisting of a leading-side lockup device for fixing the leading end of a plate and a trailing-side lockup device for fixing the trailing end of the plate is axially fixed on the bottom surface of the gap.
Each of the conventional leading- and trailing-side lockup devices comprises an elongated lockup table extending in the axial direction of the plate cylinder, a plurality of gripper plates, swingably supported at an edge portion of this lockup table by a plurality of bolts, for gripping or releasing the plate with or from the lockup table, and a plurality of cams which can be respectively engaged with gaps at the edges of the gripper plates. The plurality of cams are pivotally aligned along the axis. A plurality of compression coil springs are interposed between the lockup table and the gripper plates to bias the gripper plates in an open direction.
With the above arrangement, in order to mount a plate on a plate cylinder, when a cam shaft of the leading-side lockup device is pivoted, the gripper plates which are divided in the axial direction of the plate are released upon disengagement from the cams and are simultaneously opened by the elastic forces of the compression coil springs. An end of the plate is inserted between the leading-side lockup device and the corresponding lockup table. When the cam plate is pivoted in the direction opposite to the direction described above, the gripper plates are pivoted against the elastic forces of the compression coil springs by the behavior of the cams and are closed, thereby gripping the leading end of the plate.
The lockup table of the trailing-side lockup device is supported on the bottom surface of the circumferential gap of the plate cylinder to be movable in the circumferential direction of the plate cylinder. A plurality of plate tightening bolts are mounted at a plurality of longitudinal positions of the lockup table so that distal ends of the bolts are in contact with the wall surface of the circumferential gap of the plate cylinder.
With the above arrangement, the leading end of the plate is gripped by the leading-side lockup device as described above, the plate is wound around the circumferential surface of the plate cylinder, and the trailing end of the plate is gripped by the trailing-side lockup device. Thereafter, the tightening bolts are tightened to move the trailing-side lockup device in the circumferential direction of the plate cylinder, so that the plate is brought into tight contact with the circumferential surface of the plate cylinder. Note that since spring members are interposed between the trailing-side lockup device and the gap, the plate lockup device is moved toward the wall surface of the gap by the spring forces of the spring members upon loosening of the tightening bolts, thereby loosening the plate.
In the conventional plate lockup apparatus described above, since the plate is tightened by tightening the plurality of tightening bolts, it is difficult to uniformly tighten the plate to degrade plate mounting precision. Plate tightening and plate gripping at each operation position are cumbersome and time-consuming.